WO2016026872A1 - Imagerie parallèle par résonance magnétique à correction d'image résiduelle de nyquist pour epi - Google Patents

Imagerie parallèle par résonance magnétique à correction d'image résiduelle de nyquist pour epi Download PDF

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Publication number
WO2016026872A1
WO2016026872A1 PCT/EP2015/068973 EP2015068973W WO2016026872A1 WO 2016026872 A1 WO2016026872 A1 WO 2016026872A1 EP 2015068973 W EP2015068973 W EP 2015068973W WO 2016026872 A1 WO2016026872 A1 WO 2016026872A1
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signals
level map
image
coils
acquired
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PCT/EP2015/068973
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Elwin De Weerdt
Zhaolin Chen
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Koninklijke Philips N.V.
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Priority to US15/505,256 priority Critical patent/US10401456B2/en
Priority to DE112015003853.1T priority patent/DE112015003853T5/de
Priority to CN201580044841.5A priority patent/CN106574954B/zh
Priority to EP15751013.2A priority patent/EP3183594A1/fr
Publication of WO2016026872A1 publication Critical patent/WO2016026872A1/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
    • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
    • G01R33/561—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences
    • G01R33/5611—Parallel magnetic resonance imaging, e.g. sensitivity encoding [SENSE], simultaneous acquisition of spatial harmonics [SMASH], unaliasing by Fourier encoding of the overlaps using the temporal dimension [UNFOLD], k-t-broad-use linear acquisition speed-up technique [k-t-BLAST], k-t-SENSE
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 
    • A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves  involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
    • G01R33/34—Constructional details, e.g. resonators, specially adapted to MR
    • G01R33/341—Constructional details, e.g. resonators, specially adapted to MR comprising surface coils
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/4818—MR characterised by data acquisition along a specific k-space trajectory or by the temporal order of k-space coverage, e.g. centric or segmented coverage of k-space
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
    • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
    • G01R33/565—Correction of image distortions, e.g. due to magnetic field inhomogeneities
    • G01R33/56545—Correction of image distortions, e.g. due to magnetic field inhomogeneities caused by finite or discrete sampling, e.g. Gibbs ringing, truncation artefacts, phase aliasing artefacts
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
    • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
    • G01R33/565—Correction of image distortions, e.g. due to magnetic field inhomogeneities
    • G01R33/56554—Correction of image distortions, e.g. due to magnetic field inhomogeneities caused by acquiring plural, differently encoded echo signals after one RF excitation, e.g. correction for readout gradients of alternating polarity in EPI

Definitions

  • the invention relates to the field of magnetic resonance (MR) imaging. It concerns a method of MR imaging of at least a portion of a body.
  • the invention also relates to a MR device and to a computer program to be run on a MR device.
  • Image-forming MR methods which utilize the interaction between magnetic fields and nuclear spins in order to form two-dimensional or three-dimensional images are widely used nowadays, notably in the field of medical diagnostics, because for the imaging of soft tissue they are superior to other imaging methods in many respects, do not require ionizing radiation and are usually not invasive.
  • the body of the patient to be examined is arranged in a strong, uniform magnetic field (Bo field) whose direction at the same time defines an axis (normally the z-axis) of the co-ordinate system on which the measurement is based.
  • the magnetic field splits different energy levels for the individual nuclear spins in dependence on the magnetic field strength and the specific spin properties.
  • the spin system can be excited (spin resonance) by application of an electromagnetic alternating field (RF field, also referred to as Bi field) of defined frequency (so-called Larmor frequency, or MR frequency).
  • the distribution of the individual nuclear spins produces an overall magnetization which can be deflected out of the state of equilibrium by application of an electromagnetic pulse of appropriate radio frequency (RF pulse) while the corresponding Bi magnetic field extends perpendicular to the z-axis, so that the magnetization performs a precessional motion about the z-axis.
  • the precessional motion describes a surface of a cone whose angle of aperture is referred to as flip angle.
  • the magnitude of the flip angle is dependent on the strength and the duration of the applied electromagnetic RF pulse.
  • 90° pulse the spins are deflected from the z axis to the transverse plane (flip angle 90°).
  • the magnetization relaxes back to the original state of equilibrium, in which the magnetization in the z direction is built up again with a first time constant Ti (spin lattice or longitudinal relaxation time), and the
  • the variation of the magnetization can be detected by means of one or more receiving RF coils which are arranged and oriented within an examination volume of the MR device in such a manner that the variation of the magnetization is measured in the direction perpendicular to the z-axis.
  • the decay of the transverse magnetization is accompanied, after application of, for example, a 90° RF pulse, by a transition of the nuclear spins (induced by local magnetic field inhomogeneities) from an ordered state with the same phase to a state in which all phase angles are uniformly distributed (dephasing).
  • the dephasing can be compensated by means of a refocusing pulse (for example a 180° pulse). This produces an echo signal (spin echo) in the receiving coils.
  • the signal picked up in the receiving coils then contains components of different frequencies which can be associated with different locations in the body.
  • the MR signal data obtained via the RF coils corresponds to the spatial frequency domain and is called k-space data.
  • the k-space data are usually acquired along multiple lines with different phase encoding values to achieve sufficient coverage. Each line is digitized during read-out by collecting a number of samples. A set of k-space data is converted to a MR image by means of Fourier transformation.
  • Echo planar imaging is a known rapid MR imaging technique which is used to produce MR images at high acquisition rates, typically several images per second. It has been found particularly useful in diffusion imaging, for functional magnetic resonance imaging (fMRI), in dynamic imaging etc.
  • the basic idea of EPI is to completely sample k- space in a single repetition (single-shot EPI) during one T 2 decay, or in multiple shots (multi- shot EPI).
  • single-shot EPI all k-space lines are acquired during multiple magnetic field gradient reversals, producing multiple gradient echo signals in a single acquisition after a single RF excitation pulse, i.e., in a single measurement or "shot”.
  • multi-shot EPI the acquisition of MR signals is divided into multiple shots. In this case, k-space is segmented by multiple acquisitions. Multi-shot EPI is also referred to as segmental EPI.
  • MR images reconstructed from EPI acquisitions tend to suffer from so-called "Nyquist ghosting".
  • the ghost image is shifted by half a field of view in the phase encoding direction.
  • the ghosting pattern can be more complex.
  • the Nyquist ghost artefacts are caused mainly by induced eddy currents and system timing errors with respect to the positive and negative magnetic field gradient lobes. These errors are associated with the MR scanner hardware.
  • Reference scans may be employed to determine systematic phase errors of the MR signals induced by the imperfections of magnetic field gradient switching.
  • the imaging data can then be corrected accordingly.
  • Navigator echoes can be used, preferably in dynamic EPI scans, to track the varying delays of magnetic field gradient switching.
  • a drawback of these known techniques is that the applied corrections are generally not able to completely remove the Nyquist ghosts. This is caused by the magnetic field gradient switching delays changing over time (without being re-estimated correctly), application of only a one-dimensional phase correction (in the phase encoding direction), missing compensation of higher order terms etc.
  • a method of parallel MR imaging of at least a portion of a body placed in the examination volume of a MR device comprises the steps of:
  • Parallel imaging techniques are known in the art for accelerating MR signal acquisition.
  • a method in this category is SENSE (Sensitivity Encoding).
  • SENSE and other parallel imaging techniques use undersampled k-space data acquisition obtained from multiple RF receiving coils in parallel.
  • the (complex) signal data from the multiple RF receive coils are combined with complex weightings in such a way as to suppress undersampling artefacts (aliasing) in the finally reconstructed MR images.
  • This type of complex RF coil array signal combination is sometimes referred to as spatial filtering and includes combining in the k-space domain or in the image domain (in SENSE), as well as methods which are hybrids.
  • spatial sensitivity maps of the RF coils are typically estimated from low-resolution reference data obtained by a SENSE reference scan. This coil sensitivity information is then used to "unwrap" aliased pixels in image space using a direct inversion algorithm.
  • the gist of the invention is the application of two or more iterations of the parallel reconstruction algorithm, wherein a ghost level map indicating the level of ghosting for each image position is derived from the acquired MR signal data and the spatial sensitivity maps of the RF coils in a first iteration (step b).
  • the estimated ghost level map is then applied in a subsequent iteration of the parallel reconstruction algorithm to reconstruct the MR image, wherein the estimated ghost level map is used in step c) to eliminate the ghost artefacts in the reconstructed MR image.
  • the method of the invention further comprises the step of spatially smoothing the estimated ghost level map prior to reconstructing the MR image in step c).
  • the invention is based on the assumption of a spatially smoothly varying ghost level and hence can handle all system imperfections that lead to such a smoothly varying ghost level.
  • the assumption of a constant ghost level in the phase encoding direction is not made according to the invention.
  • the technique is fully n-dimensional, with n being the number of dimensions of the MR signal data. Hence, the technique is superior to
  • a further advantage is that the method of the invention does not require the acquisition of reference data for the removal of the Nyquist ghost artefacts. Consequently, the method of the invention provides full Nyquist artefact removal by pure post-processing of the acquired MR signal data, this is, without extending the scan time. Moreover, because no reference data is required, the technique of the invention can be advantageously used in combination with rapid dynamic imaging techniques, such as PROPELLER-DWI etc. It has to be noted, however, that, for example, in cases in which a shortest possible scan time is not essential, the method of the invention may be combined with conventional phase-correction techniques using reference data in order to further improve the level of ghost artefact removal.
  • each of steps b) and c) comprises the simultaneous computation of a MR image and a MR ghost image using a linear inversion method.
  • Linear inversion methods are conventionally applied in known parallel image reconstruction techniques (such as SENSE), for example employing least squares
  • the number of unknowns of the inversion is increased by computing not only the MR image but also the MR ghost image.
  • the ghost level map can then be estimated by computing the ratio of the reconstructed MR ghost image and the reconstructed "true" MR image in step b).
  • the MR image reconstruction in step c) involves regularisation (like in common parallel reconstruction techniques) using an (additional) regularisation constraint that is derived from the smoothed estimated ghost level map.
  • a regularisation parameter (Lagrange factor) determining the weighting of the regularisation constraint in the linear inversion can then be tuned depending on the signal-to-noise ratio (SNR) of the MR image reconstructed in step c).
  • the reconstruction method is based in this embodiment on a constrained optimization, which optimizes SNR subject to the constraint of removing the Nyquist ghost artefacts, wherein the level of ghost artefact removal may be defined interactively by a user.
  • Steps b) and c) of the method of the invention may be iteratively repeated in order to successively increase the accuracy of the ghost level map.
  • the regularisation parameter may be varied for increasing the weighting of the regularisation constraint from iteration to iteration. If the inversion problem is to ill-conditioned initially, a preliminary estimate of the ghost level map (for example obtained from a reference measurement) may be used in a first iteration, wherein the iterative scheme then converges to the true ghost level map after one or more further iterations.
  • the method of the invention may be combined with undersampling of k-space in order to increase acquisition speed.
  • the method of the invention is able to simultaneously unfold both the undersampling (aliasing) artefacts and the Nyquist ghost artefacts.
  • the method of the invention is compatible with the known compressed sensing (CS) technique, which may be applied advantageously in steps b) and/or c).
  • CS compressed sensing
  • a signal data set which has a sparse representation in a transform domain can be recovered from undersampled measurements by application of a suitable regularisation algorithm.
  • the possibility of undersampling leads to a significantly reduced acquisition time.
  • CS prescribes the conditions under which a signal data set can be reconstructed exactly or at least with high image quality even in cases in which the k-space sampling density is far below the Nyquist criterion, and it also provides the methods for such reconstruction.
  • the method of the invention described thus far can be carried out by means of a MR device including at least one main magnet coil for generating a uniform steady magnetic field within an examination volume, a number of gradient coils for generating switched magnetic field gradients in different spatial directions within the examination volume, a number of RF coils for generating RF pulses within the examination volume and/or for receiving MR signals from a body of a patient positioned in the examination volume, a control unit for controlling the temporal succession of RF pulses and switched magnetic field gradients, and a reconstruction unit for reconstructing MR images from the received MR signals.
  • the method of the invention is preferably implemented by a corresponding programming of the reconstruction unit and/or the control unit of the MR device.
  • the method of the invention can be advantageously carried out in most MR devices in clinical use at present. To this end it is merely necessary to utilize a computer program by which the MR device is controlled such that it performs the above-explained method steps of the invention.
  • the computer program may be present either on a data carrier or be present in a data network so as to be downloaded for installation in the control unit of the MR device.
  • Figure 1 schematically shows a MR device for carrying out the method of the invention
  • Figure 2 shows EPI images of a phantom reconstructed conventionally and according to the method of the invention
  • Figure 3 shows noise amplification maps for different weightings of the regularisation constraint applied according to the method of the invention
  • Figure 4 shows a ghost level map computed according to the invention.
  • a MR device 1 comprises superconducting or resistive main magnet coils 2 such that a substantially uniform, temporally constant main magnetic field Bo is created along a z-axis through an examination volume.
  • the device further comprises a set of (1 st , 2 nd , and - where applicable - 3 rd order) shimming coils 2', wherein the current flow through the individual shimming coils of the set 2' is controllable for the purpose of minimizing Bo deviations within the examination volume.
  • a magnetic resonance generation and manipulation system applies a series of RF pulses and switched magnetic field gradients (also referred to as 'gradient pulses') to invert or excite nuclear magnetic spins, induce magnetic resonance, refocus magnetic resonance, manipulate magnetic resonance, spatially and otherwise encode the magnetic resonance, saturate spins, and the like to perform MR imaging.
  • RF pulses and switched magnetic field gradients also referred to as 'gradient pulses'
  • a gradient pulse amplifier 3 applies current pulses to selected ones of whole-body gradient coils 4, 5 and 6 along x, y and z-axes of the examination volume.
  • a digital RF frequency transmitter 7 transmits RF pulses or pulse packets, via a send-/receive switch 8, to a -body RF coil 9 to transmit RF pulses into the examination volume.
  • a typical MR imaging sequence is composed of a packet of RF pulse segments of short duration which taken together with each other and any applied magnetic field gradients achieve a selected manipulation of nuclear magnetic resonance. The RF pulses are used to saturate, excite magnetic resonance, invert magnetization, refocus resonance, or manipulate resonance and select a portion of a body 10 positioned in the examination volume.
  • a set of local array RF coils 11, 12, 13 having different spatial sensitivity profiles are placed contiguous to the region selected for imaging.
  • the array RF coils 1 1, 12, 13 are used to receive MR signals induced by body-coil RF transmissions.
  • the resultant MR signals are picked up by the body RF coil 9 and by the array
  • the receiver 14 is connected to the RF coils 9, 11, 12 and 13 via send-/receive switch 8.
  • a host computer 15 controls the current flow through the shimming coils 2' as well as the gradient pulse amplifier 3 and the transmitter 7 to generate any of a plurality of MR imaging sequences, such as echo planar imaging (EPI), echo volume imaging, gradient and spin echo imaging, fast spin echo imaging, and the like.
  • EPI echo planar imaging
  • the receiver 14 receives a single or a plurality of MR data lines in rapid succession following each RF excitation pulse.
  • a data acquisition system 16 performs analog-to-digital conversion of the received signals and converts each MR data line to a digital format suitable for further processing. In modern MR devices the data acquisition system 16 is a separate computer which is specialized in acquisition of raw image data.
  • the digital raw image data is reconstructed into an image representation by a reconstruction processor 17 which applies appropriate reconstruction algorithms, such like SENSE.
  • the MR image may represent a planar slice through the patient, an array of parallel planar slices, a three-dimensional volume, or the like.
  • the image is then stored in an image memory where it may be accessed for converting slices, projections, or other portions of the image representation into appropriate format for visualization, for example via a video monitor 18 which provides a man-readable display of the resultant MR image.
  • the body 10 is subjected to a single-shot or multi- shot EPI sequence, wherein MR signals are acquired in parallel via the array of RF coils 11, 12, 13 having different spatial sensitivity profiles within the examination volume.
  • MR signals are acquired in parallel via the array of RF coils 11, 12, 13 having different spatial sensitivity profiles within the examination volume.
  • spatial sensitivity maps of the RF coils are determined from low-resolution reference data obtained by a SENSE reference scan.
  • S x) is the spatial sensitivity map of RF coil j
  • p 0bj (x) is the signal contribution from the object (the body 10)
  • p g host(x) is the signal contribution from the ghost image.
  • FOV is the size of the field of view (i.e. the "folded" field of view equal to the planned FOV divided by the acceleration factor of the parallel imaging technique).
  • Tikhonov regularisation may be used in this unfolding step as in common SENSE reconstruction. This kind of regularisation provides information about the expected level of output signal per image position. This includes information as to the image area in which the object is positioned and the background.
  • the standard Tikhonov regularisation is also applied for the ghost image p g host(xi)- It is based on the same data, with the only difference that the ghost image is shifted by one-half FOV to account for the different spatial location of the ghost image.
  • the estimated ghost level map g(x) is then calculated as: ⁇ )— PghoSt i X )/Pobj i X )
  • a further SENSE unfolding step is then performed based on the above system of equations and using the following regularisation constraint: wherein g(x) is the smoothed estimated ghost level map.
  • the finally reconstructed MR image (without Nyquist ghost artefacts) then corresponds to p 0 b/x).
  • a regularisation parameter (Lagrange factor) determining the weighting of the regularisation constraint in the second unfolding step is tuned depending on the signal-to-noise ratio of the MR image.
  • the iteration may start with a pre-set ghost level map, for example assuming a fixed ghost level or a ghost level map obtained from an initial reference measurement.
  • the total reconstruction time required by the method of the invention is only marginally increased vis-a-vis conventional SENSE, since the unfolding procedure constitutes only a small part of the total reconstruction. Moreover, the modified unfolding of the invention typically requires only a limited number of iterations.
  • Figure 2 shows EPI images of a phantom acquired with SENSE factor 2.
  • the upper left image is reconstructed without Nyquist ghost correction.
  • the image shows strong ghost artefacts.
  • Conventional one-dimensional phase correction based on a reference measurement is applied in the upper middle image.
  • the level of Nyquist ghosting is substantially reduced.
  • the upper right image is reconstructed according to the method of the invention with a low weighting of the regularisation constraint.
  • the bottom right image shows the reconstructed MR image using a strong regularisation weight.
  • the images reconstructed according to the invention show different levels of Nyquist ghost suppression.
  • Figure 3 shows corresponding noise amplification maps.
  • the noise amplification maps are computed according to:
  • HSENSE(X,)>) is the combination factor matrix obtained during the SENSE unfolding for image location x
  • y size 1 x number of RF coils
  • H c i ear (x,y) is the combination factor matrix obtained during standard SENSE unfolding with SENSE factor 1 (CLEAR operation).
  • NAM(x,y) can never be less than 1 and only provides valid information inside the imaged anatomy.
  • the upper left image in Figure 3 shows NAM(x,y ) for conventional SENSE reconstruction.
  • the upper right image corresponds to the modified SENSE unfolding with a low weighting of the regularisation constraint.
  • An intermediate regularisation weight is applied in the bottom left image, the bottom right image shows NAM(x,y) using a strong regularisation weight.
  • Figure 4 shows the ghost level map g(x,y) estimated according to the method of the invention.
  • Figure 4 illustrates that the assumption of a constant ghost level in the phase encoding direction is not made according to the invention.
  • the technique is superior to one-dimensional phase correction approaches used conventionally for Nyquist ghost removal and thus generally provides an improved image quality.

Abstract

L'invention concerne un procédé d'imagerie parallèle par RM. Le procédé comprend les étapes consistant : a) à soumettre la partie du corps (10) à une séquence d'imagerie d'au moins une impulsion RF et une pluralité de gradients de champ magnétique commutés, des signaux de résonance magnétique étant acquis en parallèle par l'intermédiaire d'une pluralité de bobines RF (11, 12, 13) ayant différents profils de sensibilité spatiale dans le volume d'examen, b) à dériver une carte de niveau d'image résiduelle estimée à partir des signaux RM acquis et des cartes de sensibilité spatiale des bobines RF (11, 12, 13), c) à reconstruire une image par RM à partir des signaux RM acquis, des cartes de sensibilité spatiale, et de la carte de niveau d'image résiduelle estimée. L'invention concerne en outre un dispositif RM (1) et un programme informatique pour un dispositif RM (1).
PCT/EP2015/068973 2014-08-22 2015-08-18 Imagerie parallèle par résonance magnétique à correction d'image résiduelle de nyquist pour epi WO2016026872A1 (fr)

Priority Applications (4)

Application Number Priority Date Filing Date Title
US15/505,256 US10401456B2 (en) 2014-08-22 2015-08-18 Parallel MR imaging with Nyquist ghost correction for EPI
DE112015003853.1T DE112015003853T5 (de) 2014-08-22 2015-08-18 Parallel-MR-Bildgebung mit Nyquist-Geisterbildkorrektur für EPI
CN201580044841.5A CN106574954B (zh) 2014-08-22 2015-08-18 针对epi的具有奈奎斯特伪影校正的并行mr成像
EP15751013.2A EP3183594A1 (fr) 2014-08-22 2015-08-18 Imagerie parallèle par résonance magnétique à correction d'image résiduelle de nyquist pour epi

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EP14181994.6 2014-08-22
EP14181994 2014-08-22

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